The Tumor and Metastasis Biology Section of the Pediatric Oncology Branch is involved in the study of the biology and therapy of metastasis, primarily in childhood cancers. Our approach to the problem of metastasis is founded in the development, characterization and use of relevant in vivo (animal) models of metastasis. These models include transplantable tumor models, genetically engineered mouse models of metastasis, and naturally occurring cancers that develop in companion animals. The breadth of in vivo expertise provided by our section provides us with a unique and informative perspective on the problem of metastasis. The study of companion animal cancers is facilitated through the Center for Cancer Research - Comparative Oncology Program (http://ccr.nci.nih.gov/resources/cop/). The use of several model systems to study problems in metastasis provides an opportunity to emphasize strengths and minimize weaknesses of a single model system.